This project represents an extension of a long-standing series of collaborative studies performed to better characterize and understand immune deficiency. Mutations involving the genes for the common gamma chain (X-SCID) and fas (ALPS) are being evaluated using dideoxyfinger printing (ddF) and direct gene sequencing. These studies have continued to identify a number of new mutations in both diseases and these data have been published and submitted for publication. In addition, this project has provided valuable experience in the critical approaches to molecular diagnosis of genetic disorders. This procedure manuals and technical approaches used, are being used to assist with the NIH CLIA resource program in areas of molecular diagnostics.